How To Look At A House

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How can I tell if a house has insulation?

Friday, September 21, 2018

All homes built in Florida in the last 20 years have insulation, and the amount of required insulation has increased regularly as the Florida Energy Code has become more stringent. But as you go backward in time from the 1990s, there is no guarantee of adequate insulation, or even any insulation at all, in an older home.

When checking insulation in a home you first want to verify if there is any. Then, if you find insulation, next determine what type it is and estimate the approximate R-value of the insulation based on the thickness of the material. There are four locations to check for insulation: floor, walls, attic, and windows. 

1) FLOOR - Most homes built in the Gainesville area since about 1960 are slab-on-grade construction. There is no insulation under the floor slab and none is necessary, because the soil beneath the slab acts as insulation. But, if the home has elevated wood floors with a crawl space under them, you can verify  floor insulation by locating and opening an access panel on the exterior wall near the ground. 

    You will need a flashlight and may have to clear away a few cobwebs before you can poke your head inside to look up at the floor framing and (hopefully!) insulation. Floor insulation was not standard when homes with elevated wood floors were built fifty or more years ago. So, if you see any fiberglass insulation batts tucked up between the floor joists, they were likely a recent improvement. 

    The R-rating of the insulation will be marked on the paper sleeve of the insulation, and is usually around R-20. The batts should be mechanically held in place by bowed strips of metal between the joists and possibly netting across the bottom of the joists. Be sure to sweep your flashlight beam across the entire area visible from the opening, looking for any insulation that has fallen down or been pulled down by critters that have gotten under the home, like in the photo below.

2) WALLS - Checking for wall insulation is a little more complicated. Because any insulation is sealed between the exterior and interior wall coverings, you will have to remove a cover plate at an electric outlet/receptacle in one or more locations at an exterior wall and peek into the small gap in the wall between the receptacle box and the wallboard to look for insulation. But, very important: before you remove any cover plates or do any probing next to the receptacle box, turn off all power to the home at the main breaker.

    It helps to shine a flashlight in the gap around the receptacle box and you may be able to get a screwdriver in the opening to expand it just a little. If you don’t find evidence of insulation at the first box or there isn’t enough opening to get a good look, move on to a second or third box to be sure.

    Walls are the least likely location to find insulation in an old house, and also the most difficult for retrofitting insulation if there is none. Unless you are planning on removing and replacing all the wallboard on the exterior walls as part of a remodeling, a hole has to be drilled in each in stud cavity above and below any firestops before insulation is blown or foamed into the cavity, Finally, each wall opening must be repaired. It’s a lot of work.

3) ATTIC - Most older homes have attic insulation and, often, there are two layers. Beneath a top layer of new blown or batt insulation is usually an older layer of original insulation that has become compressed over the years and has minimal R-value. Using a sturdy ladder to get to the attic hatch opening, remove the cover panel, and stick your head up in the attic with flashlight in hand. It is not necessary to climb into the attic. 

    You may find blown fiberglass or cellulose, older rock wool batts, or fiberglass batts. The thicker, the better. But also look for any areas of insulation that have been compressed by workmen crawling around the attic. Newer insulation installations will have a rating card near the attic opening detailing the type of material and R-value. Also, if it is blown insulation, you will also see measurement sticks at several locations (like in the photo at the top of the page) to confirm the thickness of the insulation blanket.

    Adding more attic insulation is not always a good thing, especially if it is installed incorrectly. See our blog post Should I put some more insulation in the attic?

4) WINDOWS - The insulating value of double-pane windows and sliding glass doors is typically between R-2 and R-4; not a lot, but every bit helps. To verify that windows are double-pane, hold a flashlight up against the glass at a 45º angle. The beam of light will illuminate each pane. Go to our blog post What do those numbers on the manufacturer's stickers in new windows mean? for an explanation of the different energy efficiency ratings for new windows.

   If the glass panes are cloudy, it means that the inert gas between the panes has escaped, reducing the insulation value of the window. Also, because the fogging is on the inside of the glass and not cleanable, it reduces the light transmission and appearance of the window. See our blog post Why is pressure washing double pane windows an expensive mistake? for more on this.

R-RATING - The ability of a material to resist the passage of heat through it is measured by its R-value. The higher the number, the better the insulating ability. Fiberglass batts in a 4-inch stud wall are R-11, and R-19 in a 6-inch stud wall cavity. Both fiberglass and cellulose insulation are rated at about R-3.5 per inch thickness. Here’s a chart for estimating the R-values of various materials, based on their thickness.

    The new spray foam insulations, like in the photo below, are rated at about R-6.5 per inch in closed cell version and R-3.5 for open cell, and are typically applied to the underside of the roof sheathing. 

Here’s links to a collection of our other blog posts about INSULATION: 

• What are the common problems with attic insulation?

• Why is vermiculite attic insulation a problem for both buyers and sellers of a home? 

 Why is the garage so hot in the summer?

• How can I tell if a house has insulation? 

• Why is spray foam used for attic insulation?

• Should I wrap the water heater with an insulation blanket? 

• What does the "R-Value" of home insulation mean? 

• Is pipe insulation flammable?

   Visit our INSULATION page for other related blog posts on this subject, or go to the INDEX for a complete listing of all our articles.

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